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<pre><span class="comment"> /****************************************************************************
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 ** Copyright (C) 2006-2008 Trolltech ASA. All rights reserved.
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 #include &quot;graphwidget.h&quot;
 #include &quot;edge.h&quot;
 #include &quot;node.h&quot;

 #include &lt;QDebug&gt;
 #include &lt;QGraphicsScene&gt;
 #include &lt;QWheelEvent&gt;

 #include &lt;math.h&gt;

 GraphWidget::GraphWidget()
     : timerId(0)
 {
     QGraphicsScene *scene = new QGraphicsScene(this);
     scene-&gt;setItemIndexMethod(QGraphicsScene::NoIndex);
     scene-&gt;setSceneRect(-200, -200, 400, 400);
     setScene(scene);
     setCacheMode(CacheBackground);
     setRenderHint(QPainter::Antialiasing);
     setTransformationAnchor(AnchorUnderMouse);
     setResizeAnchor(AnchorViewCenter);

     Node *node1 = new Node(this);
     Node *node2 = new Node(this);
     Node *node3 = new Node(this);
     Node *node4 = new Node(this);
     centerNode = new Node(this);
     Node *node6 = new Node(this);
     Node *node7 = new Node(this);
     Node *node8 = new Node(this);
     Node *node9 = new Node(this);
     scene-&gt;addItem(node1);
     scene-&gt;addItem(node2);
     scene-&gt;addItem(node3);
     scene-&gt;addItem(node4);
     scene-&gt;addItem(centerNode);
     scene-&gt;addItem(node6);
     scene-&gt;addItem(node7);
     scene-&gt;addItem(node8);
     scene-&gt;addItem(node9);
     scene-&gt;addItem(new Edge(node1, node2));
     scene-&gt;addItem(new Edge(node2, node3));
     scene-&gt;addItem(new Edge(node2, centerNode));
     scene-&gt;addItem(new Edge(node3, node6));
     scene-&gt;addItem(new Edge(node4, node1));
     scene-&gt;addItem(new Edge(node4, centerNode));
     scene-&gt;addItem(new Edge(centerNode, node6));
     scene-&gt;addItem(new Edge(centerNode, node8));
     scene-&gt;addItem(new Edge(node6, node9));
     scene-&gt;addItem(new Edge(node7, node4));
     scene-&gt;addItem(new Edge(node8, node7));
     scene-&gt;addItem(new Edge(node9, node8));

     node1-&gt;setPos(-50, -50);
     node2-&gt;setPos(0, -50);
     node3-&gt;setPos(50, -50);
     node4-&gt;setPos(-50, 0);
     centerNode-&gt;setPos(0, 0);
     node6-&gt;setPos(50, 0);
     node7-&gt;setPos(-50, 50);
     node8-&gt;setPos(0, 50);
     node9-&gt;setPos(50, 50);

     scale(0.8, 0.8);
     setMinimumSize(400, 400);
     setWindowTitle(tr(&quot;Elastic Nodes&quot;));
 }

 void GraphWidget::itemMoved()
 {
     if (!timerId)
         timerId = startTimer(1000 / 25);
 }

 void GraphWidget::keyPressEvent(QKeyEvent *event)
 {
     switch (event-&gt;key()) {
     case Qt::Key_Up:
         centerNode-&gt;moveBy(0, -20);
         break;
     case Qt::Key_Down:
         centerNode-&gt;moveBy(0, 20);
         break;
     case Qt::Key_Left:
         centerNode-&gt;moveBy(-20, 0);
         break;
     case Qt::Key_Right:
         centerNode-&gt;moveBy(20, 0);
         break;
     case Qt::Key_Plus:
         scaleView(1.2);
         break;
     case Qt::Key_Minus:
         scaleView(1 / 1.2);
         break;
     case Qt::Key_Space:
     case Qt::Key_Enter:
         foreach (QGraphicsItem *item, scene()-&gt;items()) {
             if (qgraphicsitem_cast&lt;Node *&gt;(item))
                 item-&gt;setPos(-150 + qrand() % 300, -150 + qrand() % 300);
         }
         break;
     default:
         QGraphicsView::keyPressEvent(event);
     }
 }

 void GraphWidget::timerEvent(QTimerEvent *event)
 {
     Q_UNUSED(event);

     QList&lt;Node *&gt; nodes;
     foreach (QGraphicsItem *item, scene()-&gt;items()) {
         if (Node *node = qgraphicsitem_cast&lt;Node *&gt;(item))
             nodes &lt;&lt; node;
     }

     foreach (Node *node, nodes)
         node-&gt;calculateForces();

     bool itemsMoved = false;
     foreach (Node *node, nodes) {
         if (node-&gt;advance())
             itemsMoved = true;
     }

     if (!itemsMoved) {
         killTimer(timerId);
         timerId = 0;
     }
 }

 void GraphWidget::wheelEvent(QWheelEvent *event)
 {
     scaleView(pow((double)2, -event-&gt;delta() / 240.0));
 }

 void GraphWidget::drawBackground(QPainter *painter, const QRectF &amp;rect)
 {
     Q_UNUSED(rect);

     <span class="comment">//</span> Shadow
     QRectF sceneRect = this-&gt;sceneRect();
     QRectF rightShadow(sceneRect.right(), sceneRect.top() + 5, 5, sceneRect.height());
     QRectF bottomShadow(sceneRect.left() + 5, sceneRect.bottom(), sceneRect.width(), 5);
     if (rightShadow.intersects(rect) || rightShadow.contains(rect))
         painter-&gt;fillRect(rightShadow, Qt::darkGray);
     if (bottomShadow.intersects(rect) || bottomShadow.contains(rect))
         painter-&gt;fillRect(bottomShadow, Qt::darkGray);

     <span class="comment">//</span> Fill
     QLinearGradient gradient(sceneRect.topLeft(), sceneRect.bottomRight());
     gradient.setColorAt(0, Qt::white);
     gradient.setColorAt(1, Qt::lightGray);
     painter-&gt;fillRect(rect.intersect(sceneRect), gradient);
     painter-&gt;setBrush(Qt::NoBrush);
     painter-&gt;drawRect(sceneRect);

     <span class="comment">//</span> Text
     QRectF textRect(sceneRect.left() + 4, sceneRect.top() + 4,
                     sceneRect.width() - 4, sceneRect.height() - 4);
     QString message(tr(&quot;Click and drag the nodes around, and zoom with the mouse &quot;
                        &quot;wheel or the '+' and '-' keys&quot;));

     QFont font = painter-&gt;font();
     font.setBold(true);
     font.setPointSize(14);
     painter-&gt;setFont(font);
     painter-&gt;setPen(Qt::lightGray);
     painter-&gt;drawText(textRect.translated(2, 2), message);
     painter-&gt;setPen(Qt::black);
     painter-&gt;drawText(textRect, message);
 }

 void GraphWidget::scaleView(qreal scaleFactor)
 {
     qreal factor = matrix().scale(scaleFactor, scaleFactor).mapRect(QRectF(0, 0, 1, 1)).width();
     if (factor &lt; 0.07 || factor &gt; 100)
         return;

     scale(scaleFactor, scaleFactor);
 }</pre>
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